1. Field of the Invention
The present invention relates generally to medical devices and, more particularly, to methods for governing bone growth.
2. Description of Related Art
A plethora of conditions fall under the general characterization of having a need to enhance bone formation or bone growth. These conditions include bone segmental defects, periodontal disease, metastatic bone disease, osteolytic bone disease and conditions where connective tissue repair would be beneficial, such as healing or regeneration of cartilage defects or injury. One particular condition characterized by a need to enhance bone growth is spinal disk injury.
Various bone inductive factors have been employed to stimulate bone growth. For example, bone morphological proteins (BMPs) are novel factors in the extended transforming growth factor beta superfamily. They were first identified by Wozney J. et al. Science (1988) 242:1528-34, using gene cloning techniques, following earlier descriptions characterizing the biological activity in extracts of demineralized bone (Urist M. Science (1965) 150:893-99). Recombinant BMP2 and BMP4 can induce new bone growth when they are injected locally into the subcutaneous tissues of rats (Wozney J. Molec Reprod Dev (1992) 32:160-67). These factors are expressed by normal osteoblasts as they differentiate, and have been shown to stimulate osteoblast differentiation and bone nodule formation in vitro as well as bone formation in vivo (Harris S. et al. J. Bone Miner Res (1994) 9:855-63).
Bone inductive factors are useful in that they can facilitate bone growth to treat a condition. However, ungoverned bone growth triggered by such bone inductive factors can also be problematic.
For example, an effective method of treating spinal disk injury is a discectomy, or surgical removal of a portion or all of an intervertebral disc followed by fusion of the adjacent vertebrae. The fusion is often accomplished by locking the adjacent vertebrae together with a spinal cage, and administering a bone inductive factor (e.g., BMP) in between the vertebrae to facilitate bone growth and fusion of the adjacent vertebrae. However, the administered bone inductive factor may cause bone growth in the spinal canal, which in turn may cause additional problems including increased intraspinal pressure and pinched nerves.
Such problems may be attenuated or eliminated with a method for governing bone growth, and directing the growth away from undesirous areas, such as areas within the spinal canal. Thus, there is a need for improved methods of governing bone growth.